1. Field of the Invention
The present invention relates to a method and apparatus for the dynamic guidance of flat products, such as flat products which are cut from a continuous web of material by a transversal cutting operation.
2. State of the Art
U.S. Pat. No. 5,029,842 discloses a signature handling apparatus including a first conveyor which sequentially moves signatures to a discharge station. At the discharge station, the signatures are sequentially transferred to a receiving conveyor. To increase the speed at which signatures can move between the first conveyor and the receiving conveyor, one or more corrugations are formed in the signatures to stiffen them. Accordingly, a corrugator assembly is located at the discharge station to stiffen the signatures by forming corrugations which extend between leading and trailing end portions of the signatures. Although the corrugations are only temporarily maintained in a signature, the corrugator assembly is close enough to the receiving conveyor that a corrugation is maintained in the signature, as the leading end portion of the signature moves to the receiving conveyor. That is, the corrugator assembly is spaced from the receiving conveyor by a distance which is less than the distance between the leading and trailing end portions of the signatures.
U.S. Pat. No. 5,107,733 discloses an apparatus for cutting and transporting a paper web in a folding apparatus of a printing press. The apparatus includes a pair of cutting cylinders for cutting web sections from the web, and a transporting device for transporting the web sections away from the cutting cylinders. The first cutting cylinder has at least one cutting anvil, and the second cutting cylinder has at least one cutting knife which meets the cutting anvil at a nip between the cutting cylinders to cut the web moving through the nip. A plurality of strips are supported on each of the first and second cutting cylinders. The strips have positions on the cutting cylinders in which they impress a temporary reinforcing profile onto each of the newly formed leading portions of the web when the strips move through the nip. The reinforcing profile is imparted to each leading portion of the web to assist in guiding the leading portion as it moves from the nip between the cutting cylinders toward the transporting device. In addition to the strips, at least one smoothing surface is also supported on each of the first cutting cylinder and the second cutting cylinder. The smoothing surfaces have positions on the cutting cylinders wherein the smoothing surfaces remove the temporary reinforcing profile from the leading portions of the web when the smoothing surfaces move through the nip.
Despite the existence of signature handling devices as described above, there has been encountered the technical problem that upon severing signatures from a continuous web during its transport to conveyor tapes, positive control of the signature is lost. After the lead edge of the signature is cut, it is fed into the in-running nip of the conveying tapes. However, geometric constraints preclude the conveying tapes from gaining control of a signature until the signature has travelled past the cutting cylinders. A crucial zone for each signature's lead edge therefore extends from behind the cutting nip to a point before the conveyor tapes gain control of the lead edge. The lead edge of the signature is unconstrained during this distance, so it can deviate from a desired straight path into the transport tapes. Particularly, in pinless folders, the signatures often deviate along curved paths instead of following an intended straight path from the cutting cylinders to the conveying tapes. These deviations can result in variations of distance between the signatures conveyed, thereby causing difficulties in further processing the signatures in a pinless folder.
Another drawback of existing cutting cylinder to tape transfers is the signatures' lead edges being blown open. This unintended opening of a signature's leading edge can cause processing jams or product damage, such as dog ears or the like.
Additional corrugating devices, such as those disclosed in U.S. Pat. No. 5,107,733, have also been used with cutting cylinders. Furthermore, the use of electrostatic tackers upstream from the cutting cylinders has been proposed to address the problems which occur during the transfer of signatures. However, these solutions cause other problems, and render the signature transfer area between cutting cylinders and conveyor tapes a rather sensitive area within a pinless folder.